Re: an aggregate array function

Merlin Moncure wrote:
> Dear hackers,
>  
> Do you think there would be any use for an aggregate which returns an
> array of the aggregated (usually simple) type?  Has this already been
> done by anyone?  I looked at the source and noticed that for each
> inserted item, the array utility functions perform a deep copy of the
> entire array (plus a reallocation).  Normally, this is no big deal, but
> if executed in the query stage, it could be kind of slow.

What exactly have you looked at? In current cvs there is array_append 
and array_cat. There *was* array_accum, but that was yanked due to an 
objection that it was redundant with the other two.

There is a contrib (intagg) that avoids the deep copy by passing 
pointers as integers, but I don't think that would be accepted as a 
builtin solution. I've considered maybe using a hash table to register 
valid pointers, but have not thought too hard about it yet. In any case 
it won't happen for 7.4.

BTW, I tried array_accum() (which is not really much different than 
array_append()) with groups of about 10,000 elements and feeding the 
array into a plr final function for a mean calculation. It was for sure 
slow compared to a native AVG() aggregate, but it wasn't that bad 
either. I don't remember the specifics, but it would be easy enough to 
try it out for yourself.

> I also noticed that null values inside is an item on the todo list.  Is anybody
> currently working on this?
>  

No one is currently working on it that I'm aware of, but I was 
considering working on it for 7.5

Joe